The present invention relates to a process for improving the stability of enzymes toward ionic surfactants by directed mutagenesis of DNA sequences coding for these enzymes and subsequent expression of these enzymes with improved ionic surfactant stability.
Enzymes such as proteases, lipases, amylases, cellulases, etc. are valuable industrial products with advantageous applications in the detergent industry because they, for example, break down enzymatically cleavable contaminants and thus facilitate easier removal of these contaminants. In order to be effective, these enzymes must not only have enzymatic activity under washing conditions (pH, temperature), but must also be compatible with other detergent ingredients, especially, for example, with surfactants. That is to say, the enzymes must have sufficient stability and sufficient activity in the presence of these substances. In this regard it is particularly the surfactants of the ionic type, which are often used in detergent and cleaner compositions, which may adversely affect the stability of the enzymes used in detergents, so that the activity of the enzymes rapidly decreases in the presence of the ionic surfactant, and the enzyme activity can hardly be utilized adequately even with short washing cycles of about 30 minutes. This inadequate utilization of the enzymatic activity during the washing or cleaning process due to the lack of stability of the enzymes toward ionic surfactants, is unfortunately the cause of distinct reductions in the washing or cleaning efficiency. Good stability of the detergent and cleaner enzymes towards ionic surfactants is particularly necessary for liquid detergent and cleaner formulations because unlike the enzyme in powdered formulations, the enzymes in liquid formulations cannot be protected by coating processes against the destabilizing effects of other ingredients of the composition such as, in particular, ionic surfactants.